1. Field of the Invention
The present invention relates to a method of pressing a blank such as a metal sheet between die and punch assemblies, and a punch and die press for carrying out such a method.
2. Description of the Prior Art
Metal sheets are generally formed into desired shapes by a means for pressing such metal sheets between a pair of press dies or punch and die assemblies. The dies employed in such a pressing method are required to be highly accurate dimensionally. Where a metal sheet to be pressed has irregular thicknesses, it tends to be cracked, wrinkled, or otherwise damaged even if it is pressed by dies of accurate dimensions.
There is known a method of pressing a blank into a complex shape with dies under the pressure of a liquid filled in the dies, as disclosed in Japanese Patent Publication No. 36-20010. With such a liquid-pressure pressing process, however, it is difficult to control the liquid pressure and it is troublesome to perform the pressing operation due to concern about possible liquid leakage.
Japanese Patent Publication No. 57-55493 discloses a process employing a resilient body such as of rubber in place of a liquid, the process being known as the Guerin process. However, since the resilient body such as of rubber fails to follow the shape of a punch highly accurately, the pressed product is liable to become cracked, wrinkled, or otherwise damaged especially when the product has a complicated configuration.